Rheumatic, connective tissue or ischemic heart diseases may heavily affect the configuration of the atrioventricular heart valves. Diseased valves may become narrow, incompetent or both. A great many patients suffering from ischemic heart disease, who previously underwent myocardial infarctions, consequently develop various degrees of mitral valve incompetence. Typically in those patients, the valve may grossly seem to be normal; yet its annulus is dilated, causing coaptation or interengagement of the leaflets to be disturbed and resulting in incompetence of the valve. Such patients will benefit from an annuloplasty as a repair, either alone or in addition to a revascularization procedure, i.e. coronary artery bypass surgery. Most but not all mitral and tricuspid valves are amenable to reconstruction, and the etiology of valvular disease has an important bearing on the indication for repair. A rheumatic valve is probably the most difficult to conserve; conversely, degenerative valves with thin and redundant tissue, elongated or ruptured chordae, and/or a dilated annulus are very likely to be repairable. Ischemic regurgitation can often be repaired with annuloplasty.
Annuloplasty rings have now become essential components of reconstructive surgery of the mitral and tricuspid valves. Their safety and durability have been proven in numerous clinical studies that have occurred since their genesis in the late 1960's when Dr. Alain Carpentier introduced the prosthetic ring. This completely rigid ring had the systolic shape of the mitral and tricuspid valve; once sutured in place, the ring permanently stabilized the valve annulus into this shape. He designed a series of multi-sized fabric-covered rings with a stainless steel or a titanium core, which were configured to approximate the original shape of the diseased or dysfunctional valve annulus. Multiple sutures were sewn around the periphery of the annulus creating an entire circle of guide lines. The ring was positioned on the valve annulus, and the guide lines were then attached to the ring and used to draw the valve opening to the configuration of the ring (which would be the approximate shape of the original valve annulus). Although Dr. Carpenter's method could significantly improve valve function, some surgeons believe that the rigid structure of rings of this type may compromise the natural flexibility of the valve components. An open or partial ring annuloplasty prosthesis is described in U.S. Pat. No. 4,164,046; it discloses a uniquely shaped open ring useful for mitral and tricuspid annuloplasty having a special velour exterior.
Subsequent experimental and clinical echocardiographic studies showed that the mitral and tricuspid annuli change continuously in size and shape during the cardiac cycle. These results induced Dr. Carlos Duran, in 1975, to develop a completely flexible ring that could adapt to such changes. His fully flexible annuloplasty ring could only be shortened in the posterior segment by the placement of placating sutures; however, judgment of the position, size and spacing of these sutures requires skill and experience. Other adjustable annuloplasty rings are described in U.S. Pat. Nos. 4,042,979 and 4,290,151. Another type of flexible ring design is shown in U.S. Pat. No. 5,450,860 which includes an open ring in the form of a wide, flexible ligament that is implanted into the valve annulus. The ligament is typically made of expanded polytetrafluoroethylene to provide flexibility, promote tissue ingrowth and allow sutures to readily pass therethrough.
Although flexible rings may avoid constraining the natural flexibility of the annulus while still improving valve function, there are some disadvantages in using flexible rings. For example, when the suture spacing along the annulus is not matched to the spacing on the ring, tension in the tissue may result and cause tissue puckering. Loss of annulus flexibility may also occur over time should scarring and stiffening of the valve annulus develop as a result of the large number of sutures needed, and such may result in a valve physiology that is similar to that of a rigid ring, somewhat compromising the natural flexibility of the valve.
Studies were also done as to determine whether these flexible annuloplasty rings would entirely correct the problems witnessed with regard to annuloplasty rings in general. As a result, it is believed that such a flexible ring may lower the risk of dehiscence because of reduced tension on sutures that would otherwise occur during systole, and such may also reduce the negative consequences of somewhat inaccurate placement of annuloplasty ring sutures, which could result in malrotation of the ring. It is also felt that such may minimize the risk of systolic anterior motion (SAM) when a left ventricular outflow tract obstruction occurs, which is a potential and fairly frequent complication associated with the use of a completely rigid ring in the mitral position. However, they still have not proved to be a complete solution to these problems.
U.S. Pat. No. 6,524,338, issued Feb. 25, 2003, shows the stapling of a flexible, generally C-shaped band that fits over the prosterior valve annulus of a mitral valve while it is being held in place in the annulus by a positioning instrument to which it is releasably sutured. Staples stored in a magazine of a stapling device are individually fed from a delivery section at spaced locations along the outer periphery of the flexible band so as to attach outer regions of the band to the heart tissue.
With the improvements in cardiopulmonary bypass and myocardial protection on one hand and in life expectancy on the other hand, an increase in interest in valve reconstructions and demand for improved novel technologies is foreseen. With careful patient selection, valve reconstruction should exhibit significant benefits compared with valve replacement, to wit: (1) decreased operative mortality and late mortality rates; (2) improved hemodynamics due to better preservation of left ventricular function; (3) fewer thromboembolic complications and reduced risk anticoagulant-related hemorrhage, particularly when compared with the installation of mechanical prostheses; (4) reduced risk of infected endocarditis; (5) greater durability leading to lower percentage of reoperations; and (6) reduced operating costs.
In summary, the prevailing techniques that are now used throughout the world, without resorting to a full valve replacement, generally employ an annuloplasty ring to reduce a great part of the circumference of the valve. This is accomplished by suturing into place an elastic, semi-rigid or rigid ring that is smaller than the native annulus being reduced; the ring may be of a closed shape or an open band or C-shape. Installation takes place using regular sutures, in much the same manner as when a full valve replacement is carried out, and the procedure may consume as much time as a full valve replacement, for example, an average of about 35 to 45 minutes. Accordingly, improved annuloplasty systems and methods of reducing this time of surgery have continued to be sought.